了解是否（！x）及其目的[重复]

x = 1 

if(x) {
 x equals true
}

but what happens when you put the ! infront:

if(!x) { 
x equals ? 
}

I see it being used lots in tutorials I read and felt I understood it. But I saw it today and it confused me again.

What does it do? What is it's purpose? why would you use it?

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This means if x==0 or x== false or not x as where !x

The exclamation mark merely means not that is a boolean negation, so

if(!x)
{
    (not x) is true, which means x is false
}

For ordinal types of x that means x == 0, for pointers x == NULL.